1. Field of the Invention
The present invention relates to a honeycomb catalyst body. More particularly, the present invention relates to a honeycomb catalyst body which can efficiently remove the fine particles contained in the exhaust gas emitted from a direct injection gasoline engine, which is low in pressure loss increase, which can eliminate the CO, HC and NOx contained in the exhaust gas, and which, during the use, hardly generates cracks in the circumference.
2. Description of Related Art
A reduction in fuel consumption of automobile is required from the standpoints of protection of global environment and resource saving. In the gasoline engine used mainly in passenger cars, direct injection of fuel is being pushed forward.
In the gasoline engine, since fuel injection from suction port has been employed, generation of soot [particulate matter (PM)] has been slight and it has caused little problem. However, in the gasoline engine of fuel direct injection type, generation of PM is greater compared to the fuel injection from suction port and a measure for not releasing the generated PM into the atmosphere has been needed.
Meanwhile, a honeycomb structure has been used as a capturing filter for removing the particulate matter (PM) discharged from the diesel engine. As the honeycomb structure used as a filter for capturing the particulate matter, there has been used a plugged honeycomb structure having plugged portions at given positions of the two end faces of the honeycomb structure (see, for example, Patent Documents 1 to 3). Here, the plugged honeycomb structure refers to a honeycomb structure having a honeycomb structure body having porous partition walls forming a plurality of divided cells each to function as a passage for fluid(exhaust gas or purified gas) and an outer wall present at the outermost peripheral portion of the honeycomb structure body, and plugged portions provided at “the open ends of given cells at the fluid (exhaust gas) inlet side end face of the honeycomb structure body” as well as at “the open ends of residual cells at the fluid (purified gas) outlet side end face of the honeycomb structure body”. In such a plugged honeycomb structure, an exhaust gas flows into cells from the exhaust gas inlet side end face; then, the exhaust gas passes through partition walls; thereafter, the exhaust gas(purified gas) is discharged from the exhaust gas outlet side end face. During the passage of exhaust gas through partition walls, the PM contained in the exhaust gas is captured by partition walls and the exhaust gas turns into a purified gas.
In such a plugged honeycomb structure, however, there have been cases that soot remains in the low-temperature portion (circumference) and causes sudden combustion because of the soot remaining. Accordingly, there has been a problem that the heat of soot combustion gives rise to local temperature rise in the peripheral portion and this local temperature rise brings about a sharp temperature gradient, causing the breakage of the peripheral portion.
As a countermeasure for such a problem, there has been used, in the diesel engine, a plugged honeycomb structure provided with plugged portions in a desired pattern so as to meet the application purpose of the structure. In, for example, the plugged honeycomb structures described in the Patent Documents 1 and 2, plugged portions are provided in such a way that each two cell ends of all the cells adjacent to the outer wall of honeycomb structure are plugged, in order to solve the problem of crack generation in the peripheral portion. By providing plugged portions in this way, no soot remains in the peripheral portion, in which temperature is lower, and the breakage of the peripheral portion is prevented.
Also, in the plugged honeycomb structure described in Patent Document 3, plugged portions are provided in the core portion (in central axis direction) of honeycomb structure in order to, for example, keep the pressure loss low while no plugged portion is provided in the portion surrounding the core portion.
Hence, it is considered to use the above-mentioned, plugged honeycomb structure used for removal of the particulate matter discharged from diesel engine, for removal of the particulate matter discharged from gasoline engine.